Repeater amplifiers of the nature taught and claimed herein find utility in a variety of applications. One such application includes point to point relay systems in which the repeater amplifier amplifies and re-transmits a microwave signal without shifting the frequencies of or otherwise changing the signals. The intermediate link provided by such a repeater amplifier, in combination with a receiving and transmitting antenna, can be utilized to overcome severe shadow losses due to terrain and distance in a microwave communications system. Another practical application for such a repeater amplifier is that of facilitating the penetration of electromagnetic radiation communications into and out of structures such as buildings and tunnels which can not ordinarily be penetrated by electromagnetic radiation broadcast from standard antenna systems.
It is conventional in a standard repeater amplifier to provide at least a pair of amplifiers for handling signals propagating in opposite directions. Each of these amplifiers is accompanied by a filter network which filters out all signals except the signals desired to be amplified. As will be recognized, such an active repeater is rather expensive in that it requires a pair of amplifiers and redundant filtering networks.
One prior art device is known which is capable of using a single broad band amplifier for amplifing the signals of different frequencies propagating in opposite directions. The filtering network which accompanies this prior art device is a complicated and expensive arrangement of bandpass filters, circulators, and isolators.
It is evident therefore that a two-way repeater amplifier which utilizes but a single broad band linear amplifier and a simple inexpensive filter network is desireable and would be especially useful in the context of radio communications systems such as are used by municipal police and fire departments. An additional and particularly attractive use is found in underground mine communication systems which require two-way repeater amplifiers to amplify the communication signals at periodic intervals along the mine passageways. Another application is in a nuclear reactor facility where a communications system must penetrate extremely thick walls of concrete and steel. The repeater-amplifier of this invention is useful here in combination with a Radiax cable to penetrate the containment building and to control the signal levels.